The Contractor will implement a 3-year longitudinal clinical trial to study the effects of mouthrinsing with stannous fluoride and sodium fluoride upon the development of dental caries, dental plaque, gingivitis, and extrinsic tooth staining. A test population of approximately 500 students will be utilized, one half of the subjects rinsing once a day in school with 10 ml. of a 0.1% solution of stannous fluoride (SnF-2) and the other half rinsing once a day in school with 10ml. of a 0,05% solution of sodium fluoride (NaF).